In the rapidly growing industries related to inkjet printing, there have been dramatic progresses in the improvement of the performance of inkjet printers and improvement of inks, which may soon make it possible to readily form high-definition, sharp images having good printability, which are comparable to silver halide photographs, even at home. Accordingly, inkjet printers have begun to be used not only at home but also in various fields such as the manufacture of large advertising boards.
The improvement of the image quality of inkjet-printed items is achieved through not only the improvement of the performances of the printers, but also the improvement of printing inks. Specifically, the improvement of a printing ink is achieved through, for example, studies of a selection of a solvent included in the ink, a selection of a dye or a pigment, and the like. Recently, attention has been focused on pigment inks, which are considered to have high color developability comparable to those of dye inks.
However, even when the pigment inks having high color developability are used, there are some cases where, for example, the pigments are peeled off from the support with time. In addition, while various materials have become used as a support on which the ink-absorbing layer is to be formed with an increase in the variety of inkjet-printed items, the ink-absorbing layers in the related art, which have insufficient adhesion to plastic films composed of polyethylene terephthalate or the like, may cause the absorbing layer to be peeled off with time.
Use of the printing methods known in the related art, such as the inkjet printing method described above and a screen printing method, in the manufacture of conductive patterns such as electronic circuits is being studied. This is because there has been a demand for high-performance, compact, thin electronic devices and accordingly there has also been a strong demand for electronic circuits and integrated circuits, which are used for producing such electronic devices, having a high density and a small thickness.
Specifically, the conductive pattern such as an electronic circuit can be produced by, for example, performing printing on the surface of a support using a conductive ink including a conductive substance such as silver by inkjet printing, screen printing, or the like, subsequently performing drying, and, as needed, performing heating or light irradiation.
However, even when printing is performed directly on the surface of a support using the conductive ink, the conductive ink, which is less likely to be adhered onto the surface of the support, may be easily peeled off, which results in, for example, breaking of wires of the final product such as an electronic circuit. In particular, while a flexible support composed of a polyimide resin, a polyethylene terephthalate resin, or the like enables bendable, flexible devices to be produced, such a support composed of a polyimide resin or the like, to which inks, resins, and the like are less likely to adhere, is likely to cause peeling to occur. This may result in breaking of wires of the final product such as an electronic circuit, which obstructs the passage of a current.
An example of known methods for addressing the above-described issues is a method in which a pattern is drawn on an ink-absorbing substrate including a latex layer disposed thereon using a conductive ink by a predetermined method in order to prepare a conductive pattern. It is known that the latex layer can be a urethane resin (e.g., see PTL 1).
However, the adhesion of the ink-absorbing layer constituting the conductive pattern, which is a latex layer, is only one step away from a level at which the conductive pattern can be used for producing electric circuits or the like.
In formation of the conductive pattern, generally, conductive substances included in the conductive ink are brought into contact with one another in order to impart electrical conductivity. Therefore, a printed item prepared by performing printing using the conductive ink is commonly fired by being heating at about 80° C. or more.
However, an ink-absorbing layer such as the latex layer described in PTL 1 above is likely to be, for example, degraded due to the heat received during the firing process. In particular, the adhesion at the interface between the ink-absorbing layer and the support is likely to be reduced, and consequently peeling may occur easily even when a small force is applied thereto.
In addition, excessive swelling, deformation, or the like of the latex layer, which serves as an ink-absorbing layer, may occur during the firing process, which results in breaking of wires or poor electric conduction of an electric circuit or the like. Furthermore, peeling may partially occur between the support and the ink-absorbing layer prior to the firing process because, in many cases, the latex layer does not have sufficient adhesion to the support before heating is performed in the firing process.
In formation of the conductive pattern, plating is commonly performed on the surface of the conductive pattern using copper or the like in order to form a high-reliability wiring pattern capable of maintaining good electrical conductivity over a prolonged period of time without, for example, causing wires to be broken.
However, plating chemicals used for plating and chemicals used in the subsequent cleaning process, which are generally strongly alkaline or strongly acidic, are likely to cause, for example, the absorbing layer or the like to be peeled off from the support, which may result in breaking of wires of a conductive pattern.
Accordingly, the conductive pattern requires high durability such that, for example, a conductive-ink-absorbing layer is not peeled off from a support even when, for example, repeatedly immersed in the above-described chemical or the like for a prolonged period of time.